Passive Modbus RTU sniffer for the **Octopus Energy Cosy heat pump.
Captures all traffic between the Cosy Hub (master) and outdoor unit (slave) via a Waveshare RS485-to-WiFi gateway in transparent transmission mode. Publishes decoded register values to Home Assistant via MQTT auto-discovery.
- Passive sniffing — zero interference with the bus, no active polling
- Auto-discovery — registers appear automatically as HA sensors
- Robust reconnection — exponential backoff on gateway disconnection
- S6 process supervision — auto-restart on crash
- CSV logging — full frame-level logs for analysis
- Operating state detection — tracks ACTIVE / HEARTBEAT / IDLE modes
- Signed int16 handling — correct negative temperature values
- Waveshare RS485-to-WiFi gateway (transparent mode, 19200 baud 8N1)
- Wired in parallel to the RS485 bus between Cosy Hub and outdoor unit
Registers are published as sensor.qsh_modbus_sniffer_* entities. See identified.md for full details and evidence, unknown.md for registers under investigation.
| Register | Name | Scale | Unit | Confidence |
|---|---|---|---|---|
| 27 | Electrical Power In | ×ばつ1 | W | CONFIRMED (r=0.999 vs Shelly EM) |
| 29 | HP LWT | ×ばつ0.1 | °C | CONFIRMED |
| 30 | Condenser Temp | ×ばつ0.1 | °C | REVISED |
| 36 | T1 External Temp | ×ばつ0.1 | °C | CONFIRMED (r=1.000 vs API) |
| 38 | Internal Unit Temp | ×ばつ0.1 | °C | STATISTICAL |
| 39 | Outdoor Ambient Temp | ×ばつ0.1 | °C | STATISTICAL |
| 40 | System Return Temp | ×ばつ0.1 | °C | CONFIRMED (tracks Shelly return) |
| 45 | Discharge Gas Temp | ×ばつ0.1 | °C | STATISTICAL (r=0.922 vs flow) |
| 47 | Flow Rate | ×ばつ0.01 | l/min | NAMED |
| 50 | Reported COP | ×ばつ0.01 | — | STATISTICAL (mean 4.23) |
| 51 | Compressor Speed | ×ばつ1 | % | STATISTICAL |
| 53 | Compressor Frequency | ×ばつ0.1 | Hz | STATISTICAL |
| 64 | Heat Output | ×ばつ1 | W | CONFIRMED (r=0.999 vs fl×ばつΔT) |
| 66 | Operating Mode | ×ばつ1 | enum | STATISTICAL |
| 91 | Target Flow Temp | ×ばつ0.1 | °C | CONFIRMED |
| Option | Default | Description |
|---|---|---|
gateway_host |
192.168.2.73 |
Waveshare gateway IP |
gateway_port |
8899 |
Gateway TCP port |
mqtt_host |
(auto) | MQTT broker (auto-detected from HA if empty) |
mqtt_port |
1883 |
MQTT port |
mqtt_user |
(auto) | MQTT username |
mqtt_pass |
(auto) | MQTT password |
publish_interval |
5 |
Seconds between MQTT publishes |
debug |
false |
Enable debug logging |
# CoP calculation template: - sensor: - name: "Cosy CoP" unit_of_measurement: "" state: > {% set heat = states('sensor.qsh_modbus_sniffer_cosy_heat_output') | float(0) %} {% set power = states('sensor.qsh_modbus_sniffer_cosy_electrical_power_in') | float(0) %} {% if power > 50 %} {{ (heat / power) | round(2) }} {% else %} 0 {% endif %}
CSV logs are written to /data/modbus_logs/ inside the add-on container, accessible via the share mount. Each day gets a separate file: modbus_YYYY-MM-DD.csv.